Photovoltaics (PV) do not require any particular maintenance and simply produces electricity using sunlight without pollution and corrosion of materials. There are various applications of PV. The technologies for building integration for using PV as exterior finishing materials have been in developing actively around the world.
In particular, building components that can be applied to integrate PV modules are very diverse, including curtain walls, ceilings, vehicles, PV roof tiles, and transparent PV windows. Depending on the characteristics, it can be used in natural light and vehicles, thus improve the overall energy saving effect, comfort, and economic feasibility of the building.
A building integrated photovoltaic (BIPV) system utilizes a location where sunlight enters the building and thus may have a structure that is combined with building components such as roofs, windows, exterior finishing materials, and the like. In particular, it is advantageous in that the structure is easy to integrate into a building, and the direction in which the incidence of sunlight can be traced is changed.
Accordingly, a solar photovoltaic window blind system that can combine shading and solar power by combining solar cell panels on sun shading plates or slats of a window blind system installed from outside to inside or from inside to outside has been proposed.
In general, if the PV window blind system is installed in a large-scale building with outer walls covered with glass, considerable renewable energy production and savings can be expected.
The PV window blind system requires a solar tracking function that follows an incident direction of sunlight to maximize solar power generation. Depending on a tracking method, the PV window blind system can be classified into a program tracking-type system and a sensor tracking-type system. The program tracking method stores and tracks the optimum sun position according to the year, month, and day using a computer or a microprocessor having a program for tracking the movement trajectory of the sun during the year. The sensor tracking method tracks the maximum incident amount using a sensor. The error may occur depending on the type and shape of the sensor.
Depending on a tracking direction, it can be classified into a slope single-axis (or horizontal single-axis) tracking system and a dual-axis tracking system. One axis of the dual-axis tracking system may trace the azimuth of the sun, and the other axis may trace an altitude angle of the sun. The slope single-axis tracking system is a system in which the axis is set at a constant inclination angle in the north-south direction and is rotated around the axis to track the sun. In the case of the slope single-axis tracking system, a power generation amount can be increased by only about 1%, even if tracking is done by the sensor method.
However, due to the nature of the window blind system, facing in the direction of the sun does not necessarily maximize the generation amount. For example, if the blind slates are toward the direction of the sun when the sun is at its meridian altitude in the mid-summer, the blind slats may be placed to be almost horizontal, and thus most areas of the blind slates may be shaded.
In addition, a wavelength range to which the optical sensor is sensitive is different from a wavelength range in which the actual power generation amount is high, and thus the identified sun direction does not necessarily guarantee the highest power generation. Furthermore, if the weather conditions are not good, a malfunction is inevitable. Accordingly, it is not cost-effective.
Solar power generation is most efficient when an angle (line) of a sunshade and a solar altitude angle (line) are orthogonal. In a general blind-type PV device, a distance between sunshades is one time “a width of the sunshade”. For preventing shading by an adjacent sunshade, an inclination angle that makes the angle of the sunshade and the solar altitude angle perpendicular to each other should be smaller than 90°. Thus, in order to practically prevent shading, the inclination angle of the sunshade and the solar altitude angle forms an angle about 14° to 76° during most of the power generation time, and thus they are not orthogonal. Accordingly, the effect of the solar tracking device is greatly reduced.
As a prior art, a distance between slats is fixed at a manufacturing stage that louver has a fixed distance and blinds are withdrawn or overlapped with the fixed space. There was no variable simultaneous spacing means for distance between the slates to solve the shading problem between slats. More specifically, in a prior art, the distance between the slates may be controlled only by overlapping slats or withdrawing the slates. The lowest end in case of a prior horizontal blind system is sequentially pulled to adjust the spaces between the slates, and accordingly, the distances between the slats cannot be variably adjusted while operating the slats.
When the distance between slats is widened, no shading may occur between the slats, light enters through space between the slats at noon. Therefore the window blind having the wide distance between slats cannot provide sufficient the shading and the lighting. In order to maintain the natural shading and the lighting of the blind, it is possible to attach the solar modules partially to the areas where the slates or louvers do not shade. However, there is a problem to make the attached area of the solar cell reduced.